This invention relates to electromechanical transducers and more particularly to an integral "H" shaped transducer employing piezoresistive elements.
The use of the well known piezoresistive effect in semiconductors has made possible the construction of electromechanical force transducers with substantially enhanced output and operating characteristics.
The technology employed is currently in step with that used in the fabrication of integrated circuits and modern day transistor technology.
Thus the prior art is replete with a plethora of technical articles and patents which describe various embodiments of such units.
A particular advantage is that by using such techniques, one can fabricate relatively small and reliable transducers to be employed in the aerospace, medical and other fields as well. The transducers can, in general, be referenced to as miniature or ultraminiature and typically have deflecting diaphragms of silicon or glass or other materials which are on the order of 0.1 inch or so in diameter with thickness between 0.0005 to 0.050 inches.
Many significant technical problems had to be overcome during the development of such devices. For example, one problem in particular, affected the resonant frequencies of the transducers. It was discovered that the leads coupled to the piezoresistor and the associated terminals had to be isolated to prevent spurious frequencies affecting the operation. A solution to such a problem is shown in U.S. Pat. No. 3,654,579 entitled "Electromechanical Transducers and Housings" patented on Apr. 4, 1972 by A. D. Kurtz, et al, and assigned to the assignee herein.
Together with the problem of lead isolation, the manufacturer was faced with further problems in the fabrication and reliable control of such miniature devices. These problems relate to mechanical stability of the device. That is, as the unit becomes smaller, the fabrication becomes more difficult. Certain of these and related problems are described and solutions as well as apparatus are offered in U.S. Pat. No. 3,739,315 entitled "Semiconductor Transducers Having H-Shaped Cross Sectional Configurations" by A. D. Kurtz, et al, issued on June 12, 1973 and assigned to the assignee herein.
This patent describes a composite transducer employing a cup and a ring which are bonded together to form an "H" shaped cross sectional unit.
In any event, there is a demand for reliability and increased performance in regard to such transducers. A major problem which has been attendant with a great deal of difficulty is the ability to "stop" or limit the movement of the diaphragm associated with such transducers for pressures applied thereto in excess of rated pressures.
Consider that the diaphragms employed in such transducers are relatively thin and small in diameter as indicated above. This fact alone makes certain prior art stop techniques inapplicable. The prior art, while cognizant of the overload problem, utilized stopping pins, or adjustable pins and screws in apertures to stop a diaphragm. Other prior art techniques involved bosses machined into the housing or elsewhere to provide stops for the diaphragm. Due to the physical size of these ultraminiature diaphragms, one could not machine to such close tolerances and hence, these stops are not possible. Another major problem in small transducers of the type described above, is that the diaphragms are typically fabricated from silicon or glass and are extremely small. These materials as silicon, glass and so on, are very brittle. Hence, the problem of stopping a small brittle diaphragm which exhibits extremely small deflection for applied pressure is considerable. Furthermore, one must be able to fabricate the diaphragm to thus maintain its size, to assure reliable operation and further assure that the stop mechanism will operate so that excessive force or pressure applied to the diaphragm will not rupture, fracture or destroy the same.
Accordingly, it is an object of the present invention to provide an improved semiconductor pressure transducer incorporating a stop mechanism, while exhibiting reliable operating characteristics.